body {
  margin: 0;
  padding: 0;
}
.container {
  margin: 50px 50px;
}
.item {
  position: relative;
  width: 100%;
  height: 500px;
}
.left {
  position: absolute;
  background: skyblue;
  width: 100px;
  height: 100%;

}
.right {
  background: orange;
  width: 100%;
  height: 100%;
  padding-left: 100px;
  box-sizing: border-box;
}